U.S. patent application number 15/348460 was filed with the patent office on 2017-05-11 for process for preparing acrylic acid from formaldehyde and acetic acid.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is BASF SE. Invention is credited to Till Christian BRUEGGEMANN, Marco HARTMANN, Michael LEJKOWSKI, Johannes LIEBERKNECHT, Yong LIU, Lukas SCHULZ, Nicolai Tonio WOERZ.
Application Number | 20170129841 15/348460 |
Document ID | / |
Family ID | 55855657 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170129841 |
Kind Code |
A1 |
HARTMANN; Marco ; et
al. |
May 11, 2017 |
PROCESS FOR PREPARING ACRYLIC ACID FROM FORMALDEHYDE AND ACETIC
ACID
Abstract
The invention relates to a process for preparing acrylic acid
from formaldehyde and acetic acid, comprising (i) providing a
gaseous stream S1 comprising formaldehyde, acetic acid and acrylic
acid, where the molar ratio of acrylic acid to the sum total of
formaldehyde and acetic acid in stream S1 is in the range from
0.005:1 to 0.3:1; (ii) contacting stream S1 with an aldol
condensation catalyst in a reaction zone to obtain a gaseous stream
S2 comprising acrylic acid.
Inventors: |
HARTMANN; Marco; (Jockgrim,
DE) ; SCHULZ; Lukas; (Mannheim, DE) ; WOERZ;
Nicolai Tonio; (Darmstadt, DE) ; LIU; Yong;
(Shanghai, CN) ; BRUEGGEMANN; Till Christian;
(Ludwigshafen, DE) ; LEJKOWSKI; Michael;
(Neckargemuend, DE) ; LIEBERKNECHT; Johannes;
(Limburgerhof, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen am Rhein |
|
DE |
|
|
Assignee: |
BASF SE
Ludwigshafen am Rhein
DE
|
Family ID: |
55855657 |
Appl. No.: |
15/348460 |
Filed: |
November 10, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62253699 |
Nov 11, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 27/198 20130101;
C07C 51/353 20130101; C07C 51/43 20130101; C07C 57/04 20130101;
C07C 51/347 20130101; C07C 51/353 20130101; B01J 35/1019 20130101;
B01J 35/002 20130101; B01J 29/7057 20130101; C07C 57/04
20130101 |
International
Class: |
C07C 51/353 20060101
C07C051/353; C07C 51/43 20060101 C07C051/43 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2015 |
DE |
10 2015 222 180.6 |
Claims
1. A process for preparing acrylic acid from formaldehyde and
acetic acid, comprising (i) providing a gaseous stream S1
comprising formaldehyde, acetic acid and acrylic acid, where the
molar ratio of acrylic acid to the sum total of formaldehyde and
acetic acid in stream S1 is in the range from 0.005:1 to 0.3:1;
(ii) contacting stream S1 with an aldol condensation catalyst in a
reaction zone to obtain a gaseous stream S2 comprising acrylic
acid.
2. The process according to claim 1, wherein the molar ratio of
acrylic acid to the sum total of formaldehyde and acetic acid in
stream S1 in (i) is in the range from 0.02:1 to 0.1:1.
3. The process according to claim 1, wherein the molar ratio of
acetic acid:formaldehyde in stream S1 in (i) is in the range from
0.25:1 to 4.4:1.
4. The process according to claim 1, wherein at least 65% by volume
of stream S1 in (i) consists of formaldehyde, acetic acid, acrylic
acid, water and inert gas.
5. The process according to claim 1, further comprising (iii)
partly condensing stream S2 obtained in (ii) by cooling it down to
a temperature in the range from 0 to 200.degree. C., with
separation of stream S2 into a condensed stream S2a and an
uncondensed stream S2b, with optional intermediate storage of
stream S2a in a buffer vessel.
6. The process according to claim 5, wherein stream S2b is at least
partly recycled into the reaction zone in (ii).
7. The process according to claim 5, wherein the acrylic acid
content of stream S2b is in the range from 0.01% to 0.5% by volume,
based on the total volume of stream S2b.
8. The process according to claim 5, further comprising (iv)
working up stream S2a to obtain a product stream SP comprising
acrylic acid and a recycling stream SR comprising acrylic acid,
where the recycling stream SR comprises not more than 10% of the
acrylic acid present in stream S2.
9. The process according to claim 8, wherein at least a portion of
the recycling stream SR is recycled into the reaction zone in
(ii).
10. The process according to claim 1, wherein stream S1 comprises a
stream comprising formaldehyde and acetic acid, of the recycling
stream SR and optionally of stream S2b.
11. The process according to claim 8, wherein the workup in (iv)
comprises (iv.1) removing a portion of the acrylic acid present in
stream S2a from stream S2a to obtain a stream S3 depleted of
acrylic acid relative to stream S2a, and a stream S4 enriched in
acrylic acid relative to stream S2a, comprising acrylic acid and
acetic acid; (iv.2) removing a portion of the acrylic acid present
in stream S4 from stream S4 to obtain a stream S5 depleted of
acrylic acid relative to stream S4, comprising acrylic acid and
acetic acid, and a stream S6 enriched in acrylic acid relative to
stream S4, comprising acrylic acid.
12. The process according to claim 11, wherein the acrylic acid
content of stream S3 is in the range from 0.01% to 5% by weight,
based on the total weight of stream S3.
13. The process according to claim 11, wherein the acrylic acid
content of stream S5 is in the range from 0.1% to 30% by weight,
based on the total weight of stream S5.
14. The process according to claim 11, wherein stream S5, at least
in part, is at least part of the recycling stream SR which is
recycled into the reaction zone in (ii).
15. The process according to claim 11, wherein stream S3, at least
in part, is at least part of the recycling stream SR which is
recycled into the reaction zone in (ii).
Description
[0001] The present invention relates to a process for preparing
acrylic acid from formaldehyde and acetic acid, comprising the
providing of a gaseous stream S1 comprising formaldehyde, acetic
acid and acrylic acid, where the molar ratio of acrylic acid to the
sum total of formaldehyde and acetic acid in stream S1 is in the
range from 0.005:1 to 0.3:1 and the contacting of stream S1 with an
aldol condensation catalyst is effected in a reaction zone to
obtain a gaseous stream S2 comprising acrylic acid.
[0002] The preparation of acrylic acid from formaldehyde and acetic
acid in an aldol condensation with the aid of an aldol condensation
catalyst generally gives significant amounts of unwanted
byproducts, combined with an unsatisfactory selectivity in terms of
acrylic acid formation and the associated yield of acrylic
acid.
[0003] Vitcha and Sims, I & EC Product Research and
Development, Vol. 5, No. 1, March 1966, pages 50 to 53, state that,
in the synthesis of acrylic acid in a gas phase reaction proceeding
from acetic acid and formaldehyde at a molar ratio of 8:1 to 10:1,
high conversions and yields of acrylic acid were observed. While
this excess of acetic acid leads to a higher yield of acrylic acid,
this results simultaneously in an incomplete acetic acid conversion
which, in order to be able to operate such a preparation process in
an economically viable manner, entails an appropriate workup of the
product stream and associated apparatus complexity.
[0004] Complete separation of acrylic acid from the product stream
cannot sensibly be achieved in an industrial process. However, it
is necessary to feed at least portions of the product stream still
comprising unconverted reactants back to the process. It has been
found here that acrylic acid at the reactor inlet and the
reintroduction of acrylic acid into the reaction zone adversely
affect both the further conversion and the selectivity of acrylic
acid formation.
[0005] It was therefore an object of the present invention to
provide an improved process for preparing acrylic acid from
formaldehyde and acetic acid, especially with regard to selectivity
in terms of acrylic acid formation and the associated yield of
acrylic acid, in the case of recycling of portions of the product
stream into the reaction zone.
[0006] It has been found that, surprisingly, such a process can be
provided by setting the molar ratio of acrylic acid to the sum
total of formaldehyde and acetic acid in stream S1 within a defined
range.
[0007] The present invention therefore relates to a process for
preparing acrylic acid from formaldehyde and acetic acid,
comprising [0008] (i) providing a gaseous stream S1 comprising
formaldehyde, acetic acid and acrylic acid, where the molar ratio
of acrylic acid to the sum total of formaldehyde and acetic acid in
stream S1 is in the range from 0.005:1 to 0.3:1; [0009] (ii)
contacting stream S1 with an aldol condensation catalyst in a
reaction zone to obtain a gaseous stream S2 comprising acrylic
acid.
[0010] The process of the invention enables achievement of a higher
selectivity in terms of acrylic acid formation and an associated
increased yield of acrylic acid at a molar ratio of acrylic acid to
the sum total of formaldehyde and acetic acid in stream S1 within a
defined range.
Providing a Stream S1 in (i)
[0011] In step (i) of the present process, a gaseous stream S1
comprising formaldehyde, acetic acid and acrylic acid, where the
molar ratio of acrylic acid to the sum total of formaldehyde and
acetic acid in stream S1 is in the range from 0.005:1 to 0.3:1, is
provided.
[0012] Preferably, the molar ratio of acrylic acid to the sum total
of formaldehyde and acetic acid in stream S1 in (i) is in the range
from 0.02:1 to 0.1:1, preferably in the range from 0.025:1 to
0.09:1, further preferably in the range from 0.03:1 to 0.08:1,
further preferably in the range from 0.035:1 to 0.07:1.
[0013] In principle, stream S1 is not restricted in terms of the
molar ratio of formaldehyde:acetic acid. Preferably, the molar
ratio of acetic acid:formaldehyde in stream S1 in (i) is not less
than 0.25:1. Likewise preferably, the molar ratio of acetic
acid:formaldehyde in stream S1 in (i) is not more than 4.4:1.
[0014] Further preferably, the molar ratio of acetic
acid:formaldehyde in stream S1 in (i) is in the range from 0.25:1
to 4.4:1, further preferably in the range from 0.5:1 to 2:1,
further preferably in the range from 0.8:1 to 1.2:1.
[0015] Useful sources for the acetic acid in principle include any
suitable source comprising at least a proportion of acetic acid.
This may be acetic acid fed fresh to the process. It may likewise
be acetic acid which has not been converted in the above-described
process and which, for example after removal from the product
stream in one or more workup steps, is recycled into the process. A
combination of acetic acid fed fresh to the process and acetic acid
recycled into the process is likewise possible. It is likewise
possible to use acetic acid adducts, for example acetic
anhydride.
[0016] Useful sources for formaldehyde likewise in principle
include any suitable source comprising at least a proportion of
formaldehyde. This may be formaldehyde fed fresh to the process. It
may likewise be formaldehyde which has not been converted in the
above-described process and which, for example after removal from
the product stream in one or more workup steps, is recycled into
the process. A combination of formaldehyde fed fresh to the process
and formaldehyde recycled into the process is likewise possible.
For example, the source used for the formaldehyde may be an aqueous
formaldehyde solution (formalin). It is likewise possible to use a
formaldehyde source which affords formaldehyde, for instance
trioxane or paraformaldehyde.
[0017] Preferably, the source used for the formaldehyde is an
aqueous formaldehyde solution. Preferably, the aqueous formaldehyde
solution has a formaldehyde content in the range from 20% to 85% by
weight, preferably from 30% to 80% by weight, further preferably
from 40% to 60% by weight.
[0018] In principle, stream S1 is not restricted in terms of the
molar ratio of acrylic acid to formaldehyde, provided that the
molar ratio of acrylic acid to the sum total of formaldehyde and
acetic acid is observed. Preferably, the molar ratio of acrylic
acid to formaldehyde in stream S1 in (i) is in the range from
0.01:1 to 0.6:1, preferably in the range from 0.04:1 to 0.2:1,
further preferably in the range from 0.05:1 to 0.18:1, further
preferably in the range from 0.07:1 to 0.14:1.
[0019] It is conceivable in principle that stream S1 in (i)
consists of formaldehyde, acetic acid and acrylic acid.
[0020] Preferably, stream S1 comprises at least one further
component in addition to formaldehyde, acetic acid and acrylic
acid, and stream S1 in (i) further preferably additionally
comprises water, or inert gas, or water and inert gas.
[0021] Preferably, stream S1 in (i) additionally comprises water.
In principle, stream S1 is not restricted in terms of the molar
ratio of water to formaldehyde. Preferably, in stream S1 in (i),
the molar ratio of water to formaldehyde is in the range from 2:1
to 0.5:1, preferably in the range from 1.7:1 to 0.6:1, further
preferably in the range from 1.5:1 to 0.7:1.
[0022] It is conceivable in principle that stream S1 consists of
formaldehyde, acetic acid, acrylic acid and water.
[0023] Preferably, stream S1 in (i) additionally comprises inert
gas. In principle, stream S1 is not subject to any particular
restrictions in terms of the inert gas content. Preferably, the
inert gas content of stream S1 in (i) is in the range from 0.1% to
85.0% by volume, preferably in the range from 40% to 75% by volume,
further preferably in the range from 50% to 70% by volume, based on
the total volume of stream S1.
[0024] In the context of the present invention, inert gas shall be
all the materials that are gaseous under the process conditions
selected in each case and are inert in stage (i). "Inert" in this
context means that the gaseous material in a single pass through
the reaction zone is converted to an extent of less than 5 mol %,
preferably to an extent of less than 2 mol %, more preferably to an
extent of less than 1 mol %. Regardless of this definition, water,
oxygen, carbon dioxide, carbon monoxide, propionic acid, formic
acid, methanol, methyl acetate, acetaldehyde, methyl acrylate,
ethene, acetone and methyl formate shall not be covered by the term
"inert gas". In this context, the term "inert gas" as used in this
context of present invention refers either to a single gas or to a
mixture of two or more gases. For example, useful inert gases
include helium, neon, argon, krypton, radon, xenon, nitrogen,
sulfur hexafluoride and gas mixtures of two or more thereof.
[0025] Preferably, the inert gas in stream S1 in (i) comprises
nitrogen, there being no restrictions in principle with regard to
the proportion of nitrogen. Preferably, at least 95% by weight,
further preferably at least 98% by weight, further preferably at
least 99% by weight, of the inert gas in stream S1 in (i) consists
of nitrogen.
[0026] It is conceivable in principle that stream S1 in (i)
consists of formaldehyde, acetic acid, acrylic acid and inert gas.
It is further conceivable that stream S1 in (i) consists of
formaldehyde, acetic acid, acrylic acid, water and inert gas.
[0027] Preferably, at least 65% by volume and preferably at least
80% by volume of stream S1 in (i) consists of formaldehyde, acetic
acid, acrylic acid, water and inert gas.
[0028] Preferably, stream S1 in (i) additionally comprises one or
more of the compounds oxygen, carbon dioxide, carbon monoxide,
propionic acid, formic acid, methanol, methyl acetate,
acetaldehyde, methyl acrylate, ethene, acetone and methyl
formate.
Aldol Condensation Catalyst
[0029] The term "aldol condensation catalyst" in the present
context is understood to mean any catalyst capable of catalyzing an
aldol condensation of the two compounds formaldehyde and acetic
acid to give acrylic acid.
[0030] In principle, all suitable aldol condensation catalysts are
useful in accordance with the invention. Examples, used as
unsupported catalysts or in supported form, are alkali metal or
alkaline earth metal oxides, mixed oxides comprising vanadium
oxide, aluminosilicates or zeolites. Preferably, the aldol
condensation catalyst comprises vanadium and optionally phosphorus
and optionally oxygen, and also optionally tungsten.
[0031] In a preferred configuration, the aldol condensation
catalyst comprises vanadium, phosphorus and oxygen, further
preferably a vanadium phosphorus oxide.
[0032] Moreover, the aldol condensation catalyst in (ii) comprises
a vanadium phosphorus oxide V.sub.xP.sub.yO.sub.z where the x:y
weight ratio is preferably in the range from 1:0.5 to 1:5, further
preferably from 1:0.7 to 1:4, more preferably from 1:0.8 to 1:3,
and the x:z weight ratio is preferably in the range from 1:0.1 to
1:10, further preferably in the range from 1:0.5 to 1:9, more
preferably in the range from 1:0.8 to 1:8.
[0033] In a further preferred configuration, the aldol condensation
catalyst comprises vanadium, phosphorus and oxygen, and
additionally tungsten. Further preferably, in this configuration,
the aldol condensation catalyst comprises an oxidic composition
comprising vanadium, tungsten, phosphorus, oxygen and optionally
tin, where the molar ratio of phosphorus to the sum total of
vanadium, tungsten and any tin in the oxidic composition is in the
range from 1.4:1 to 2.4:1.
[0034] The aldol condensation catalyst can be used in the form of
an unsupported catalyst or in supported form on one or more
substances preferably selected from the group consisting of
SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3 and ZrO.sub.2 and mixtures of
two or more thereof, further preferably in the form of a supported
catalyst.
[0035] The aldol condensation catalyst may be present, for example,
as granules or extrudates in the form of cylinders, spheres, hollow
cylinders, in star form, in tablet form or as a mixture thereof.
Preferably, the aldol condensation catalyst is in the form of
extrudates, the cross section of the extrudates having a
rectangular, triangular, hexagonal, square, polygonal, oval or
circular shape. Particular preference is given to using an aldol
condensation catalyst in extrudates with a round cross section, the
diameter of the round cross-sectional area being in the range from
0.1 to 100 mm, preferably in the range from 0.2 to 80 mm, further
preferably in the range from 0.5 to 50 mm, further preferably in
the range from 1 to 30 mm, and the length of the extrudates being
in the range from 0.1 to 100 mm, preferably in the range from 0.5
to 80 mm, further preferably in the range from 1 to 70 mm.
Contacting of Stream S1 with an Aldol Condensation Catalyst in
(ii)
[0036] The contacting of stream S1 with an aldol condensation
catalyst in (ii) in a reaction zone to obtain a gaseous stream S2
comprising acrylic acid is preferably effected continuously.
[0037] The contacting in (ii) is preferably effected in at least
one reactor, preferably in at least two reactors, further
preferably in at least two reactors connected in parallel, which
are preferably operated in alternation, the reactors preferably
being fixed bed reactors. In the alternating mode of operation, at
least one reactor is always in operation. The fixed bed reactors
are configured, for example, as shell and tube reactors or
thermoplate reactors. In the case of a shell and tube reactor, the
catalytically active fixed bed is advantageously within the
catalyst tubes, with fluid heat carrier flowing around them.
[0038] The catalyst hourly space velocity with regard to the
contacting in (ii) in the reactor is preferably chosen such that a
balanced ratio of the parameters of conversion, selectivity,
space-time yield, reactor geometry and reactor dimensions can be
achieved.
[0039] Preferably, the contacting in (ii) in a fixed bed reactor is
effected at a catalyst hourly space velocity in the range from 0.01
to 50 kg/(h*kg), preferably in the range from 0.1 to 40 kg/(h*kg),
further preferably in the range from 0.5 to 30 kg/(h*kg), the
catalyst hourly space velocity being defined as the mass of stream
S1 in kg per hour and per unit mass of aldol condensation catalyst
in kg.
[0040] The contacting in (ii) in the reactor is not subject to any
particular restrictions with regard to the temperature of the
catalyst bed, provided that the contacting of stream S1 with the
aldol condensation catalyst gives a stream S2 comprising acrylic
acid. Preferably, the contacting in (ii) in a fixed bed reactor is
effected at a temperature of the catalyst bed in the range from 200
to 450.degree. C., preferably in the range from 250 to 400.degree.
C., further preferably in the range from 300 to 400.degree. C.
[0041] The contacting in (ii) in the reactor is not subject to any
particular restrictions with regard to the pressure, provided that
the contacting of stream S1 with the aldol condensation catalyst
gives a stream S2 comprising acrylic acid. Preferably, the
contacting in (ii) is effected at an absolute pressure in the range
from 0.5 to 5 bar, further preferably in the range from 0.8 to 3
bar, further preferably in the range from 1 to 1.8 bar.
[0042] Stream S1 may in principle be fed to the reaction zone at
any temperature suitable for the process of the invention.
Preferably, stream S1 is fed to the reaction zone at a temperature
at which it is entirely in gaseous form. Further preferably, stream
S1 is fed to the reaction zone at a temperature in the range from
150 to 450.degree. C., further preferably from 200 to 400.degree.
C., further preferably from 250 to 390.degree. C.
[0043] Preferably, the stream S2 obtained in (ii) is at a
temperature in the range from 200 to 450.degree. C., preferably in
the range from 250 to 400.degree. C., further preferably in the
range from 300 to 400.degree. C.
Separation of Stream S2
[0044] Preferably, the process according to the present invention
additionally comprises [0045] (iii) partly condensing stream S2
obtained in (ii) by cooling it down to a temperature, preferably in
the range from 0 to 200.degree. C., further preferably in the range
from 20 to 150.degree. C., further preferably in the range from 30
to 80.degree. C., with separation of stream S2 into a condensed
stream S2a and an uncondensed stream S2b, with optional
intermediate storage of stream S2a in a buffer vessel.
[0046] Preferably, stream S2 additionally comprises inert gas, and
stream S2a is depleted in terms of inert gas with respect to stream
S2b.
[0047] The expression "depleted in terms of inert gas" as used in
the context of the present invention for stream S2a with respect to
stream S2b means that the proportion by weight of inert gas, based
on the total weight of stream S2a, is less than the proportion by
weight of inert gas based on the total weight of stream S2b.
[0048] Preferably, stream S2b is at least partly recycled into the
reaction zone in (ii).
[0049] With regard to stream S2b, preferably at least 80% by
volume, preferably at least 90% by volume, consists of inert gas,
carbon dioxide and carbon monoxide.
[0050] The acrylic acid content of stream S2b is preferably in the
range from 0.01% to 0.5% by volume, further preferably in the range
from 0.02% to 0.2% by volume, further preferably in the range from
0.05% to 0.15% by volume, based on the total volume of stream
S2b.
[0051] Preferably, stream S2b comprises not more than 5%,
preferably from 1% to 5%, of the acrylic acid present in stream
S2.
[0052] Preferably, in the process of the present invention, a
portion of stream S2b is discharged from the process as purge
stream. This purge stream preferably comprises not more than 30%,
further preferably not more than 20%, of the total amount of stream
S2b.
[0053] Preferably, stream S2a has an acrylic acid content of at
least 15% by weight, preferably in the range from 20% to 60% by
weight, further preferably in the range from 25% to 50% by weight,
based on the total weight of stream S2a.
[0054] Stream S2a preferably comprises acrylic acid and
formaldehyde, further preferably acrylic acid, formaldehyde and
water, further preferably acrylic acid, formaldehyde, water and
acetic acid.
[0055] Preferably, at least 90% by weight, preferably from 90% to
99% by weight, further preferably from 95% to 99% by weight, of
stream S2a consists of acrylic acid, formaldehyde, water and acetic
acid.
[0056] The weight ratio of acrylic acid:water in stream S2a is
preferably in the range from 0.5:1 to 2.0:1, further preferably in
the range from 0.8:1 to 1.8:1, further preferably in the range from
1.0:1 to 1.5:1.
[0057] Preferably, in stream S2a, the weight ratio of acrylic acid
to acetic acid is in the range from 1.0:1 to 2.5:1, preferably in
the range from 1.5:1 to 2.3:1, further preferably in the range from
1.7:1 to 2.1:1.
[0058] The weight ratio of acrylic acid to formaldehyde in stream
2a is preferably in the range from 2:1 to 8:1, further preferably
in the range from 3:1 to 7:1, further preferably in the range from
3.5:1 to 5:1.
[0059] Preferably, stream S2a additionally comprises one or more of
the compounds acetaldehyde, methanol, methyl acrylate, methyl
acetate, ethene, acetone, nitrogen, carbon dioxide and carbon
monoxide. Preferably, the total content of these compounds in
stream S2a is preferably not more than 10% by weight, further
preferably from 0.1% to 8% by weight, further preferably from 0.5%
to 5% by weight.
Workup of Stream S2a
[0060] Preferably, the process according to the present invention
additionally comprises [0061] (iv) working up stream S2a to obtain
a product stream SP comprising acrylic acid and a recycling stream
SR comprising acrylic acid, where the recycling stream SR comprises
not more than 10% of the acrylic acid present in stream S2.
[0062] Preferably, the recycling stream SR comprises 1% to 10%,
preferably from 1% to 5%, of the acrylic acid present in stream
S2.
[0063] In a preferred configuration of the process of the present
invention, at least a portion of the recycling stream SR is
recycled into the reaction zone in (ii).
[0064] In principle, it is thus conceivable that either the
recycling stream SR or stream S2b, or both streams (SR+S2b), are
fed to the reaction zone in (ii). Preferably, both streams SR and
S2b are fed to the reaction zone in (ii).
[0065] Preferably, stream S1 consists of a stream comprising
formaldehyde and acetic acid, of the recycling stream SR and
preferably additionally of stream S2b.
[0066] Preferably, the workup in (iv) in the process of the present
invention comprises [0067] (iv.1) removing a portion of the acrylic
acid present in stream S2a from stream S2a to obtain a stream S3
depleted of acrylic acid relative to stream S2a, preferably
comprising formaldehyde and water, and a stream S4 enriched in
acrylic acid relative to stream S2a, comprising acrylic acid and
acetic acid; [0068] (iv.2) removing a portion of the acrylic acid
present in stream S4 from stream S4 to obtain a stream S5 depleted
of acrylic acid relative to stream S4, comprising acrylic acid and
acetic acid, and a stream S6 enriched in acrylic acid relative to
stream S4, comprising acrylic acid.
[0069] The expression "depleted of acrylic acid" as used in the
context of the present invention with regard to stream S3 and
stream S2a means that the proportion by weight of acrylic acid,
based on the total weight of stream S3, is less than the proportion
by weight of acrylic acid based on the total weight of stream S2a.
The expression "enriched in acrylic acid" as used in this context
of the present invention with regard to stream S4 and stream S2a
means that the proportion by weight of acrylic acid, based on the
total weight of stream S4, is greater than the proportion by weight
of acrylic acid in stream S2a.
[0070] Equally, the expression "depleted of acrylic acid" as used
in the context of the present invention with regard to stream S5
and stream S4 means that the proportion by weight of acrylic acid,
based on the total weight of stream S5, is less than the proportion
by weight of acrylic acid based on the total weight of stream S4.
The expression "enriched in acrylic acid" as used in this context
of the present invention with regard to stream S6 and stream S4
means that the proportion by weight of acrylic acid, based on the
total weight of stream S6, is greater than the proportion by weight
of acrylic acid in stream S4.
[0071] The removing in (iv.1) in the process of the present
invention is preferably effected by rectification. For
rectificative separation, it is possible in principle to use any
suitable apparatus or any suitable combination of apparatuses.
Preference is given to using at least one column, further
preferably one or two columns, further preferably one column,
preferably equipped with separating internals.
[0072] In principle, the at least one column for the removing in
(iv.1) is not restricted in terms of theoretical plates, provided
that the described removing in (iv.1) is achieved. Preferably, the
column has 5 to 50, preferably 10 to 40 and further preferably 15
to 30 theoretical plates.
[0073] In principle, the removing in (iv.1) can be effected at any
suitable pressure, provided that the described removing in (iv.1)
is achieved. Preferably, the removing in (iv.1) is effected at a
pressure at the top of the column in the range from 0.1 to 2.0 bar,
preferably in the range from 0.2 to 1.8 bar, further preferably in
the range from 0.3 to 1.5 bar.
[0074] In principle, the removing in (iv.1) can be effected at any
suitable temperature, provided that the described removing in
(iv.1) is achieved. Preferably, the removing in (iv.1) is effected
at a temperature in the bottom of the column in the range from 50
to 180.degree. C., preferably in the range from 60 to 170.degree.
C., further preferably in the range from 80 to 150.degree. C.
[0075] Preferably, stream S3 is withdrawn from the top of the
column in (iv.1).
[0076] Stream S4 is preferably withdrawn from the bottom of the
column in (iv.1).
[0077] Preferably, the acrylic acid content of stream S3 is in the
range from 0.01% to 5% by weight, preferably in the range from
0.05% to 3% by weight, further preferably in the range from 0.1% to
2% by weight, based on the total weight of stream S3.
[0078] Preferably, the acrylic acid content of stream S4 is in the
range from 40% to 80% by weight, preferably in the range from 45%
to 75% by weight, further preferably in the range from 50% to 70%
by weight, based on the total weight of stream S4.
[0079] Preferably, in stream S4, the weight ratio of acrylic
acid:acetic acid is in the range from 4.0:1 to 0.5:1, preferably in
the range from 3.5:1 to 0.8:1, further preferably in the range from
3.0:1 to 1.0:1.
[0080] Preferably, at least 80% by weight, preferably at least 90%
by weight and further preferably at least 95% by weight of stream
S4 consists of acrylic acid and acetic acid.
[0081] Preferably, stream S4 comprises one or more of the compounds
formic acid, propionic acid, water, formaldehyde and methanol.
[0082] Preferably, the removing in (iv.2) is effected by
rectification. For rectificative removal, it is possible in
principle to use any suitable apparatus or any suitable combination
of apparatuses. Preference is given to using at least one column,
further preferably one or two columns, further preferably one
column, preferably equipped with separating internals.
[0083] In principle, the at least one column for the removing in
(iv.2) is not restricted in terms of theoretical plates, provided
that the described removing in (iv.2) is achieved. Preferably, the
column has 5 to 50, preferably 10 to 40 and further preferably 15
to 30 theoretical plates.
[0084] In principle, the removing in (iv.2) can be effected at any
suitable pressure, provided that the described removing in (iv.2)
is achieved. Preferably, the removing in (iv.2) is effected at a
pressure at the top of the column in the range from 0.01 to 1.0
bar, preferably in the range from 0.02 to 0.8 bar, further
preferably in the range from 0.05 to 0.5 bar.
[0085] In principle, the removing in (iv.2) can be effected at any
suitable temperature, provided that the described removing in
(iv.2) is achieved. Preferably, the removing in (iv.2) is effected
at a temperature in the bottom of the column in the range from 50
to 180.degree. C., preferably in the range from 60 to 170.degree.
C., further preferably in the range from 70 to 150.degree. C.
[0086] Stream S5 is preferably withdrawn from the top of the column
in (iv.2).
[0087] Preferably, the acrylic acid content of stream S5 is in the
range from 0.1% to 30% by weight, preferably in the range from 0.5%
to 25% by weight, further preferably in the range from 1.0% to 20%
by weight, based on the total weight of stream S5.
[0088] Preferably, in stream S5, the weight ratio of acrylic
acid:acetic acid is in the range from 0.001:1 to 0.20:1, preferably
in the range from 0.005:1 to 0.15:1, further preferably in the
range from 0.01:1 to 0.12:1.
[0089] Preferably, at least 85% by weight, preferably at least 90%
by weight and further preferably at least 95% by weight of stream
S5 consists of acrylic acid and acetic acid.
[0090] Preferably, stream S5 comprises one or more of the compounds
formic acid, propionic acid, water, formaldehyde and methanol.
[0091] Preferably, stream S5, at least in part, preferably in full,
is at least part of the recycling stream SR which is recycled into
the reaction zone in (ii).
[0092] Preferably, stream S3, at least in part, is at least part of
the recycling stream SR which is recycled into the reaction zone in
(ii).
[0093] In principle, it is thus conceivable that either S5 or S3,
or both, is/are at least part of the recycling stream SR.
Preferably, both S5 and S3 form at least part of the recycling
stream SR.
Stream S6
[0094] Preferably, at least 90% by weight, preferably from 95% to
99.9% by weight, further preferably from 98% to 99.5% by weight, of
stream S6 consists of acrylic acid.
[0095] Preferably, stream S6 additionally comprises acetic acid,
where the acetic acid content of stream S6 is not more than 10% by
weight, preferably from 0.1% to 5% by weight, further preferably
from 0.2% to 2% by weight.
[0096] Preferably, in the process of the present invention, stream
S6 is the product stream SP.
[0097] Preferably, the removing in (iv.2) is effected by
rectification. For rectificative removal, it is possible in
principle to use any suitable apparatus or any suitable combination
of apparatuses. Preference is given to using at least one column,
further preferably one or two columns, further preferably one
column, preferably equipped with separating internals. Stream S6 is
preferably withdrawn as a side draw from the column or from the
bottom of the column, preferably as a side draw from the column
(iv.2).
Stream S3
[0098] With regard to S3, at least 80% by weight, preferably from
80% to 99% by weight, further preferably from 85% to 95% by weight,
of this stream S3 consists of formaldehyde and water.
[0099] Preferably, the weight ratio of formaldehyde to water in
stream S3 is in the range from 0.05:1 to 1:1, preferably in the
range from 0.05:1 to 0.8:1, further preferably in the range from
0.1:1 to 0.5:1.
[0100] Preferably, stream S3 additionally comprises one or more of
the compounds acrylic acid, acetic acid, acetaldehyde, methanol,
methyl acrylate, methyl acetate, ethene, acetone, methyl formate,
carbon dioxide and carbon monoxide. The total content of these
compounds in stream S3 is preferably not more than 10% by weight,
further preferably from 1% to 10% by weight, further preferably
from 2% to 10% by weight.
Separation of Stream S3
[0101] Preferably, the workup in (iv) additionally comprises [0102]
(iv.3) at least partly separating stream S3 into a
formaldehyde-enriched stream S8 and a formaldehyde-depleted stream
S7.
[0103] The expression "depleted of formaldehyde" as used in the
context of the present invention with regard to stream S7 and
stream S3 means that the proportion by weight of formaldehyde,
based on the total weight of stream S7, is less than the proportion
by weight of formaldehyde based on the total weight of stream S3.
The expression "enriched in formaldehyde" as used in this context
of the present invention with regard to stream S8 and stream S3
means that the proportion by weight of formaldehyde, based on the
total weight of stream S8, is greater than the proportion by weight
of formaldehyde in stream S3.
[0104] Preferably, at least 70% by weight, preferably from 70% to
98% by weight, further preferably from 75% to 95% by weight, of
stream S8 consists of formaldehyde and water.
[0105] Preferably, the weight ratio of formaldehyde to water in
stream S8 is in the range from 0.25:1 to 2.0:1, preferably in the
range from 0.5:1 to 1.5:1, further preferably in the range from
0.75:1 to 1.25:1.
[0106] Preferably, stream S8 additionally comprises acrylic acid,
where the acrylic acid content of stream S8 is not more than 5% by
weight, preferably from 0.1% to 5% by weight, further preferably
0.2% to 3% by weight.
[0107] Preferably, stream S8 additionally comprises at least one
compound selected from the group consisting of acetic acid,
acetaldehyde, methanol, methyl acrylate, methyl acetate, ethene,
acetone and methyl formate. Preferably, the total content of these
compounds in stream S8 is not more than 20% by weight, preferably
from 2% to 20% by weight, further preferably from 3% to 18% by
weight.
[0108] Preferably, at least 85% by weight, preferably from 90% to
99.9% by weight, further preferably from 95% to 99% by weight, of
stream S7 consists of water and formaldehyde.
[0109] Preferably, stream S7 additionally comprises at least one of
the compounds acrylic acid, acetic acid, acetaldehyde, methanol,
methyl acrylate, methyl acetate, ethene, acetone and methyl
formate. Preferably is the total content of these compounds in
stream S7 not more than 15% by weight, preferably from 1% to 5% by
weight.
[0110] Preferably, the separating in (iv.3) is effected by
rectification. For rectificative removal, it is possible in
principle to use any suitable apparatus or any suitable combination
of apparatuses. Preference is given to using at least one column,
further preferably one or two columns, further preferably one
column, equipped with separating internals.
[0111] In principle, the at least one column for the removing in
(iv.3) is not restricted in terms of theoretical plates, provided
that the described removing in (iv.3) is achieved. Preferably, the
column has 5 to 50, preferably 10 to 40 and further preferably 15
to 30 theoretical plates.
[0112] In principle, the removing in (iv.3) can be effected at any
suitable pressure, provided that the removing in (iv.3) is
achieved. Preferably, the separating in (iv.3) is effected at a
pressure at the top of the column in the range from 0.01 to 2 bar,
preferably in the range from 0.02 to 1.5 bar, further preferably in
the range from 0.05 to 1.0 bar.
[0113] In principle, the removing in (iv.3) can be effected at any
suitable temperature, provided that the removing in (iv.3) is
achieved. Preferably, the separating in (iv.3) is effected at a
temperature in the bottom of the column in the range from 30 to
180.degree. C., preferably in the range from 40 to 150.degree. C.,
further preferably in the range from 50 to 120.degree. C.
[0114] Preferably, stream S8 is withdrawn from the bottom of the
column in (iv.3).
[0115] Preferably, stream S7 is withdrawn from the top of the
column in (iv.3).
[0116] Preferably, stream S8, at least in part, preferably in full,
is at least part of the recycling stream SR which is recycled into
the reaction zone in (ii).
[0117] In principle, it is thus conceivable that either S5 or S3 or
S8, or S5 with S8 or S3 with S8, or all three (S3, S5, S8) is/are
at least part of the recycling stream SR. Preferably, both S5 and
S3 and S8 form at least part of the recycling stream SR.
[0118] Preferably, stream S5 and stream S8 are recycled together
into the reaction zone in (ii).
[0119] As described in detail above, the present invention provides
a highly integrated process for preparing acrylic acid in which
numerous streams and partial streams can be recycled into the
reaction zone, in which case these recycling operations drastically
reduce the use of fresh reactants. At the same time, the molar
ratio of acrylic acid to the sum total of formaldehyde and acetic
acid is adjusted such that, in spite of the presence of acrylic
acid, a high selectivity in terms of acrylic acid formation and an
associated high yield of acrylic acid are achieved. This
illustrates that the process of the invention provides an
exceptionally finely adjusted, well-balanced overall process,
beginning with the aldol condensation of formaldehyde and acetic
acid and ending with the removal of the acrylic acid-comprising
product stream, which takes account of all the chemical and
energetic specifics of acrylic acid preparation and configures them
advantageously in all aspects.
[0120] The present invention is illustrated in detail by the
following embodiments and combinations of embodiments which are
apparent from the corresponding dependency references and other
references: [0121] 1. A process for preparing acrylic acid from
formaldehyde and acetic acid, comprising [0122] (i) providing a
gaseous stream S1 comprising formaldehyde, acetic acid and acrylic
acid, where the molar ratio of acrylic acid to the sum total of
formaldehyde and acetic acid in stream S1 is in the range from
0.005:1 to 0.3:1; [0123] (ii) contacting stream S1 with an aldol
condensation catalyst in a reaction zone to obtain a gaseous stream
S2 comprising acrylic acid. [0124] 2. The process according to
embodiment 1, wherein the molar ratio of acrylic acid to the sum
total of formaldehyde and acetic acid in stream S1 in (i) is in the
range from 0.02:1 to 0.1:1, preferably in the range from 0.025:1 to
0.09:1, further preferably in the range from 0.03:1 to 0.08:1,
further preferably in the range from 0.035:1 to 0.07:1. [0125] 3.
The process according to embodiment 1 or 2, wherein the molar ratio
of acetic acid:formaldehyde in stream S1 in (i) is not less than
0.25:1. [0126] 4. The process according to any of embodiments 1 to
3, wherein the molar ratio of acetic acid:formaldehyde in stream S1
in (i) is not more than 4.4:1. [0127] 5. The process according to
any of embodiments 1 to 4, wherein the molar ratio of acetic
acid:formaldehyde in stream S1 in (i) is in the range from 0.25:1
to 4.4:1, preferably in the range from 0.5:1 to 2:1, further
preferably in the range from 0.8:1 to 1.2:1. [0128] 6. The process
according to any of embodiments 1 to 5, wherein the molar ratio of
acrylic acid to formaldehyde in stream S1 in (i) is in the range
from 0.01:1 to 0.6:1, preferably in the range from 0.04:1 to 0.2:1,
further preferably in the range from 0.05:1 to 0.18:1, further
preferably in the range from 0.07:1 to 0.14:1. [0129] 7. The
process according to any of embodiments 1 to 6, wherein stream S1
in (i) additionally comprises water. [0130] 8. The process
according to embodiment 7, wherein, in stream S1 in (i), the molar
ratio of water to formaldehyde is in the range from 2:1 to 0.5:1,
preferably in the range from 1.7:1 to 0.6:1, further preferably in
the range from 1.5:1 to 0.7:1. [0131] 9. The process according to
any of embodiments 1 to 8, wherein stream S1 in (i) additionally
comprises inert gas. [0132] 10. The process according to embodiment
9, wherein the inert gas content of stream S1 in (i) is in the
range from 0.1% to 85.0% by volume, preferably in the range from
40% to 75% by volume, further preferably in the range from 50% to
70% by volume, based on the total volume of stream S1. [0133] 11.
The process according to embodiment 9 or 10, wherein the inert gas
in stream S1 in (i) comprises nitrogen, and preferably at least 95%
by weight, further preferably at least 98% by weight, further
preferably at least 99% by weight, of the inert gas consists of
nitrogen. [0134] 12. The process according to any of embodiments 1
to 11, wherein at least 65% by volume and preferably at least 80%
by volume of stream S1 in (i) consists of formaldehyde, acetic
acid, acrylic acid, water and inert gas. [0135] 13. The process
according to any of embodiments 1 to 12, wherein stream S1 in (i)
additionally comprises one or more of the compounds oxygen, carbon
dioxide, carbon monoxide, propionic acid, formic acid, methanol,
methyl acetate, acetaldehyde, methyl acrylate, ethene, acetone and
methyl formate. [0136] 14. The process according to any of
embodiments 1 to 13, wherein the aldol condensation catalyst in
(ii) comprises a vanadium phosphorus oxide V.sub.xP.sub.yO.sub.z
where the x:y weight ratio is preferably in the range from 1:0.5 to
1:5, further preferably from 1:0.7 to 1:4, more preferably from
1:0.8 to 1:3, and the x:z weight ratio is preferably in the range
from 1:0.1 to 1:10, further preferably in the range from 1:0.5 to
1:9, more preferably in the range from 1:0.8 to 1:8. [0137] 15. The
process according to any of embodiments 1 to 13, wherein the aldol
condensation catalyst in (ii) comprises an oxidic composition
comprising vanadium, tungsten, phosphorus, oxygen and optionally
tin, where the molar ratio of phosphorus to the sum total of
vanadium, tungsten and any tin in the oxidic composition is in the
range from 1.6:1 to 2.4:1. [0138] 16. The process according to
embodiment 14 or 15, wherein the aldol condensation catalyst is
used in the form of an unsupported catalyst or in supported form on
one or more substances, preferably selected from the group
consisting of SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3 and ZrO.sub.2
and mixtures of two or more thereof, preferably in the form of a
supported catalyst. [0139] 17. The process according to any of
embodiments 1 to 16, wherein the contacting in (ii) is effected
continuously. [0140] 18. The process according to any of
embodiments 1 to 17, wherein the contacting in (ii) is effected in
at least one reactor, preferably in at least two reactors, further
preferably in at least two reactors connected in parallel, which
are preferably operated in alternation, the reactors preferably
being fixed bed reactors. [0141] 19. The process according to
embodiment 16, wherein the contacting in (ii) in a fixed bed
reactor is effected at a catalyst hourly space velocity in the
range from 0.01 to 50 kg/(h*kg), preferably in the range from 0.1
to 40 kg/(h*kg), further preferably in the range from 0.5 to 30
kg/(h*kg), the catalyst hourly space velocity being defined as the
mass of stream S1 in kg per hour and per unit mass of aldol
condensation catalyst in kg. [0142] 20. The process according to
embodiment 18 or 19, wherein the contacting in (ii) is effected in
a fixed bed reactor at a temperature of the catalyst bed in the
range from 200 to 450.degree. C., preferably in the range from 250
to 400.degree. C., further preferably in the range from 300 to
400.degree. C., and at an absolute pressure in the range from 0.5
to 5 bar, further preferably in the range from 0.8 to 3 bar,
further preferably in the range from 1 to 1.8 bar. [0143] 21. The
process according to any of embodiments 1 to 20, wherein the stream
S2 obtained in (ii) is at a temperature in the range from 200 to
450.degree. C., preferably in the range from 250 to 400.degree. C.,
further preferably in the range from 300 to 400.degree. C. [0144]
22. The process according to any of embodiments 1 to 21,
additionally comprising [0145] (iii) partly condensing stream S2
obtained in (ii) by cooling it down to a temperature, preferably in
the range from 0 to 200.degree. C., further preferably in the range
from 20 to 150.degree. C., further preferably in the range from 30
to 80.degree. C., with separation of stream S2 into a condensed
stream S2a and an uncondensed stream S2b,
[0146] with optional intermediate storage of stream S2a in a buffer
vessel. [0147] 23. The process according to embodiment 22, wherein
stream S2 additionally comprises inert gas, and stream S2a is
depleted in terms of inert gas with respect to stream S2b. [0148]
24. The process according to embodiment 22 or 23, wherein stream
S2b is at least partly recycled into the reaction zone in (ii).
[0149] 25. The process according to any of embodiments 22 to 24,
wherein at least 80% by volume and preferably at least 90% by
volume of stream S2b consists of inert gas, carbon dioxide and
carbon monoxide. [0150] 26. The process according to any of
embodiments 22 to 25, wherein the acrylic acid content of stream
S2b is in the range from 0.01% to 0.5% by volume, preferably in the
range from 0.02% to 0.2% by volume, further preferably in the range
from 0.05% to 0.15% by volume, based on the total volume of stream
S2b. [0151] 27. The process according to any of embodiments 22 to
26, wherein stream S2b comprises not more than 5%, preferably from
1% to 5%, of the acrylic acid present in stream S2. [0152] 28. The
process according to any of embodiments 22 to 25, wherein a portion
of stream S2b is removed from the process as purge stream and this
purge stream is preferably not more than 30%, further preferably
not more than 20%, of the total amount of stream S2b. [0153] 29.
The process according to any of embodiments 22 to 28, wherein
stream S2a has an acrylic acid content of at least 15% by weight,
preferably in the range from 20% to 60% by weight, further
preferably in the range from 25% to 50% by weight, based on the
total weight of stream S2a. [0154] 30. The process according to any
of embodiments 22 to 29, wherein stream S2a comprises acrylic acid
and formaldehyde, preferably acrylic acid, formaldehyde and water,
further preferably acrylic acid, formaldehyde, water and acetic
acid. [0155] 31. The process according to embodiment 30, wherein at
least 90% by weight, preferably from 90% to 99% by weight, further
preferably from 95% to 99% by weight, of stream S2a consists of
acrylic acid, formaldehyde, water and acetic acid. [0156] 32. The
process according to embodiment 30 or 31, wherein the weight ratio
of acrylic acid:water in stream S2a is in the range from 0.5:1 to
2.0:1, preferably in the range from 0.8:1 to 1.8:1, further
preferably in the range from 1.0:1 to 1.5:1. [0157] 33. The process
according to either of embodiments 32 and 33, wherein the weight
ratio of acrylic acid to acetic acid in stream S2a is in the range
from 1.0:1 to 2.5:1, preferably in the range from 1.5:1 to 2.3:1,
further preferably in the range from 1.7:1 to 2.1:1. [0158] 34. The
process according to any of embodiments 30 to 33, wherein the
weight ratio of acrylic acid to formaldehyde in stream S2a is in
the range from 2:1 to 8:1, preferably in the range from 3:1 to 7:1,
further preferably in the range from 3.5:1 to 5:1. [0159] 35. The
process according to any of embodiments 30 to 34, wherein stream
S2a additionally comprises one or more of the compounds
acetaldehyde, methanol, methyl acrylate, methyl acetate, ethene,
acetone, nitrogen, carbon dioxide and carbon monoxide, where the
total content of these compounds in stream S2a is preferably not
more than 10% by weight, further preferably from 0.1% to 8% by
weight, further preferably from 0.5% to 5% by weight. [0160] 36.
The process according to any of embodiments 22 to 35, preferably
according to any of embodiments 22 to 35, additionally comprising
[0161] (iv) working up stream S2a to obtain a product stream SP
comprising acrylic acid and a recycling stream SR comprising
acrylic acid, where the recycling stream SR comprises not more than
10% of the acrylic acid present in stream S2. [0162] 37. The
process according to embodiment 36, wherein the recycling stream SR
comprises 1% to 10%, preferably from 1% to 5%, of the acrylic acid
present in stream S2. [0163] 38. The process according to
embodiment 36 or 37, wherein at least a portion of the recycling
stream SR is recycled into the reaction zone in (ii). [0164] 39.
The process according to embodiment 38, wherein stream S1 consists
of a stream comprising formaldehyde and acetic acid, of the
recycling stream SR and preferably additionally of stream S2b.
[0165] 40. The process according to either of embodiments 36 and
37, wherein the workup in (iv) comprises [0166] (iv.1) removing a
portion of the acrylic acid present in stream S2a from stream S2a
to obtain a stream S3 depleted of acrylic acid relative to stream
S2a, preferably comprising formaldehyde and water, and a stream S4
enriched in acrylic acid relative to stream S2a, comprising acrylic
acid and acetic acid; [0167] (iv.2) removing a portion of the
acrylic acid present in stream S4 from stream S4 to obtain a stream
S5 depleted of acrylic acid relative to stream S4, comprising
acrylic acid and acetic acid, and a stream S6 enriched in acrylic
acid relative to stream S4, comprising acrylic acid. [0168] 41. The
process according to embodiment 40, wherein the removing in (iv.1)
is effected by rectification, preferably using at least one column,
further preferably one or two columns, further preferably one
column, preferably equipped with separating internals. [0169] 42.
The process according to embodiment 41, wherein the column has 5 to
50, preferably 10 to 40, further preferably 15 to 30, theoretical
plates. [0170] 43. The process according to embodiment 41 or 42,
wherein the removing in (iv.1) is effected at a pressure at the top
of the column in the range from 0.1 to 2.0 bar, preferably in the
range from 0.2 to 1.8 bar, further preferably in the range from 0.3
to 1.5 bar. [0171] 44. The process according to any of embodiments
41 to 43, wherein the removing in (iv.1) is effected at a
temperature in the bottom of the column in the range from 50 to
180.degree. C., preferably in the range from 60 to 170.degree. C.,
further preferably in the range from 80 to 150.degree. C. [0172]
45. The process according to any of embodiments 41 to 44, wherein
stream S3 is withdrawn from the top of the column in (iv.1). [0173]
46. The process according to either of embodiments 44 and 45,
wherein stream S4 is withdrawn from the bottom of the column in
(iv.1). [0174] 47. The process according to any of embodiments 40
to 46, wherein the acrylic acid content of stream S3 is in the
range from 0.01% to 5% by weight, preferably in the range from
0.05% to 3% by weight, further preferably in the range from 0.1% to
2% by weight, based on the total weight of stream S3. [0175] 48.
The process according to any of embodiments 40 to 47, wherein the
acrylic acid content of stream S4 is in the range from 40% to 80%
by weight, preferably in the range from 45% to 75% by weight,
further preferably in the range from 50% to 70% by weight, based on
the total weight of stream S4. [0176] 49. The process according to
any of embodiments 40 to 48, wherein the weight ratio of acrylic
acid:acetic acid in stream S4 is in the range from 4.0:1 to 0.5:1,
preferably in the range from 3.5:1 to 0.8:1, further preferably in
the range from 3.0:1 to 1.0:1. [0177] 50. The process according to
any of embodiments 40 to 49, wherein at least 80% by weight,
preferably at least 90% by weight, further preferably at least 95%
by weight, of stream S4 consists of acrylic acid and acetic acid.
[0178] 51. The process according to any of embodiments 40 to 50,
wherein stream S4 comprises one or more of the compounds formic
acid, propionic acid, water, formaldehyde and methanol. [0179] 52.
The process according to any of embodiments 40 to 51, wherein the
removing in (iv.2) is effected by rectification, preferably using
at least one column, further preferably one or two columns, further
preferably one column, preferably equipped with separating
internals. [0180] 53. The process according to embodiment 52,
wherein the column has 5 to 50, preferably 10 to 40, further
preferably 15 to 30, theoretical plates. [0181] 54. The process
according to embodiment 52 or 53, wherein the removing in (iv.2) is
effected at a pressure at the top of the column in the range from
0.01 to 1.0 bar, preferably in the range from 0.02 to 0.8 bar,
further preferably in the range from 0.05 to 0.5 bar. [0182] 55.
The process according to any of embodiments 52 to 54, wherein the
removing in (iv.2) is effected at a temperature in the bottom of
the column in the range from 50 to 180.degree. C., preferably in
the range from 60 to 170.degree. C., further preferably in the
range from 70 to 150.degree. C. [0183] 56. The process according to
any of embodiments 52 to 55, wherein stream S5 is withdrawn from
the top of the column in (iv.2). [0184] 57. The process according
to any of embodiments 40 to 56, wherein the acrylic acid content of
stream S5 is in the range from 0.1% to 30% by weight, preferably in
the range from 0.5% to 25% by weight, further preferably in the
range from 1.0% to 20% by weight, based on the total weight of
stream S5. [0185] 58. The process according to any of embodiments
40 to 57, wherein the weight ratio of acrylic acid:acetic acid in
stream S5 is in the range from 0.001:1 to 0.20:1, preferably in the
range from 0.005:1 to 0.15:1, further preferably in the range from
0.01:1 to 0.12:1. [0186] 59. The process according to any of
embodiments 40 to 58, wherein at least 85% by weight, preferably at
least 90% by weight, further preferably at least 95% by weight, of
stream S5 consists of acrylic acid and acetic acid. [0187] 60. The
process according to any of embodiments 40 to 59, wherein stream S5
comprises one or more of the compounds formic acid, propionic acid,
water, formaldehyde and methanol. [0188] 61. The process according
to any of embodiments 40 to 60, wherein stream S5, at least in
part, preferably in full, is at least part of the recycling stream
SR which is recycled into the reaction zone in (ii). [0189] 62. The
process according to any of embodiments 40 to 61, wherein stream
S3, at least in part, is at least part of the recycling stream SR
which is recycled into the reaction zone in (ii). [0190] 63. The
process according to any of embodiments 40 to 62, wherein at least
90% by weight, preferably from 95% to 99.9% by weight, further
preferably from 98% to 99.5% by weight, of stream S6 consists of
acrylic acid. [0191] 64. The process according to embodiment 63,
wherein stream S6 additionally comprises acetic acid, where the
acetic acid content of stream S6 is not more than 10% by weight,
preferably from 0.1% to 5% by weight, further preferably from 0.2%
to 2% by weight. [0192] 65. The process according to any of
embodiments 40 to 64, wherein stream S6 is the product stream SP.
[0193] 66. The process according to any of embodiments 40 to 65,
wherein the removing in (iv.2) is effected by rectification,
preferably using at least one column, further preferably one or two
columns, further preferably one column, preferably equipped with
separating internals, and wherein stream S6 is withdrawn as side
draw from the column or from the bottom of the column, preferably
as side draw from the column (iv.2). [0194] 67. The process
according to any of embodiments 40 to 66, wherein at least 80% by
weight, preferably from 80% to 99% by weight, further preferably
from 85% to 95% by weight, of stream S3 consists of formaldehyde
and water. [0195] 68. The process according to embodiment 67,
wherein the weight ratio of formaldehyde to water in stream S3 is
in the range from 0.05:1 to 1:1, preferably in the range from
0.05:1 to 0.8:1, further preferably in the range from 0.1:1 to
0.5:1. [0196] 69. The process according to embodiment 67 or 68,
wherein stream S3 additionally comprises one or more of the
compounds acrylic acid, acetic acid, acetaldehyde, methanol, methyl
acrylate, methyl acetate, ethene, acetone, methyl formate, carbon
dioxide and carbon monoxide, where the total content of these
compounds in stream S3 is preferably not more than 10% by weight,
further preferably from 1% to 10% by weight, further preferably
from 2% to 10% by weight. [0197] 70. The process according to any
of embodiments 40 to 69, wherein the workup in (iv) additionally
comprises [0198] (iv.3) at least partly separating stream S3 into a
formaldehyde-enriched stream S8 and a formaldehyde-depleted stream
S7. [0199] 71. The process according to embodiment 70, wherein at
least 70% by weight, preferably from 70% to 98% by weight, further
preferably from 75% to 95% by weight, of stream S8 consists of
formaldehyde and water. [0200] 72. The process according to
embodiment 71, wherein the weight ratio of formaldehyde to water in
stream S8 is in the range from 0.25:1 to 2.0:1, preferably in the
range from 0.5:1 to 1.5:1, further preferably in the range from
0.75:1 to 1.25:1. [0201] 73. The process according to any of
embodiments 70 to 72, wherein stream S8 additionally comprises
acrylic acid, where the acrylic acid content of stream S8 is not
more than 5% by weight, preferably from 0.1% to 5% by weight,
further preferably from 0.2% to 3% by weight. [0202] 74. The
process according to any of embodiments 70 to 73, wherein stream S8
additionally comprises at least one compound selected from the
group consisting of acetic acid, acetaldehyde, methanol, methyl
acrylate, methyl acetate, ethene, acetone and methyl formate, where
the total content of these compounds in stream S8 is not more than
20% by weight, preferably from 2% to 20% by weight, further
preferably from 3% to 18% by weight. [0203] 75. The process
according to any of embodiments 70 to 74, wherein at least 85% by
weight, preferably from 90% to 99.9% by weight, further preferably
from 95% to 99% by weight, of stream S7 consists of water and
formaldehyde. [0204] 76. The process according to any of
embodiments 70 to 75, wherein stream S7 additionally comprises at
least one of the compounds acrylic acid, acetic acid, acetaldehyde,
methanol, methyl acrylate, methyl acetate, ethene, acetone and
methyl formate, where the total content of these compounds in
stream S7 is not more than 15% by weight, preferably from 1% to 5%
by weight. [0205] 77. The process according to any of embodiments
70 to 76, wherein the separating in (iv.3) is effected by
rectification, preferably using at least one column, further
preferably one or two columns, further preferably one column,
equipped with separating internals. [0206] 78. The process
according to embodiment 77, wherein the column has 5 to 50,
preferably 10 to 40, further preferably 15 to 30, theoretical
plates. [0207] 79. The process according to embodiment 77 or 78,
wherein the separating in (iv.3) is effected at a pressure at the
top of the column in the range from 0.01 to 2 bar, preferably in
the range from 0.02 to 1.5 bar, further preferably in the range
from 0.05 to 1.0 bar. [0208] 80. The process according to any of
embodiments 77 to 79, wherein the separating in (iv.3) is effected
at a temperature in the bottom of the column in the range from 30
to 180
.degree. C., preferably in the range from 40 to 150.degree. C.,
further preferably in the range from 50 to 120.degree. C. [0209]
81. The process according to any of embodiments 77 to 80, wherein
stream S8 is withdrawn from the bottom of the column in (iv.3).
[0210] 82. The process according to any of embodiments 77 to 81,
wherein stream S7 is withdrawn from the top of the column in
(iv.3). [0211] 83. The process according to any of embodiments 70
to 82, wherein stream S8, at least in part, preferably in full, is
at least part of the recycling stream SR which is recycled into the
reaction zone in (ii). [0212] 84. The process according to any of
embodiments 70 to 83, wherein stream S5 and stream S8 are recycled
together into the reaction zone in (ii).
[0213] U.S. Provisional Patent Application No. 62/253,699, filed
Nov. 11, 2015, is incorporated into the present application by
literature reference. With regard to the abovementioned teachings,
numerous changes and deviations from the present invention are
possible. It can therefore be assumed that the invention, within
the scope of the appended claims, can be performed differently from
the way described specifically herein.
DESCRIPTION OF THE FIGURES
[0214] FIG. 1 shows, in schematic form, a flow diagram of the
process of the invention, i.e. including the experimental set up
according to example 2, with a reaction unit comprising an aldol
condensation catalyst and streams S1 to S8. As well as the
recycling stream SR (not shown), the recycling stream S2b (S2b_rec)
is preferably present. The recycling stream SR is preferably
composed of stream S3, and any further streams S5 and/or S8. In the
case of simultaneous use of S5 and S8, they can, as shown, be
recycled via a common conduit; an alternative option is recycling
via two separate conduits (not shown).
[0215] FIG. 2 shows a plot of the acrylic acid yield based on the
formaldehyde conversion in % (ordinate, from 0% to 35%) versus the
molar ratio of acrylic acid to the sum total of formaldehyde and
acetic acid (reactants) in stream S1 (abscissa, from 0 to 0.12
vol/vol) for experiment 1 with the results from tables 1-4.
[0216] FIG. 3 shows a plot of the acrylic acid yield based on the
acetic acid conversion in % (ordinate) versus the molar ratio of
acrylic acid to the sum total of formaldehyde and acetic acid
(reactants) in stream S1 (abscissa, from 0 to 0.12 vol/vol) for
experiment 1 with the results from tables 1-4.
[0217] FIG. 4 shows a plot of the relative preparation costs for
acrylic acid (ordinate, from 100% to 110%) versus the molar ratio
of acrylic acid to the sum total of formaldehyde and acetic acid in
stream S1 (abscissa, 0 to 0.3 vol/vol).
[0218] The present invention is illustrated in detail by the
examples which follow.
EXAMPLES
I. Analysis
I.1 Gas Chromatography
[0219] For gas chromatography, an instrument of the Agilent 7890
type with an FFAP column was used. The temperature program was as
follows: [0220] hold at 40.degree. C. for 10 min; [0221] heat to
90.degree. C. at a heating rate of 2 K/min; [0222] heat to
200.degree. C. at a heating rate of 6 K/min; [0223] heat to
250.degree. C. at a heating rate of 25 K/min; [0224] hold at
250.degree. C. for 10 min.
I.2 X-Ray Diffractometry (XRD)
[0225] X-ray diffractograms (Cu K alpha radiation) were recorded on
a D8 Advance series 2 diffractometer from Bruker AXS. The
diffractometer was equipped with a divergence aperture opening of
0.1.degree. and a Lynxeye detector. On the abscissa is plotted the
angle (2 theta), and on the ordinate the signal intensity (Lin
(counts)).
I.3 BET Measurements
[0226] The specific BET surface areas were determined by means of
nitrogen adsorption at 77 K to DIN 66131.
II. Preparation of the Catalysts
II.1 Catalyst 1
[0227] Oxidic catalyst comprising vanadium and phosphorus on silica
support
[0228] The catalyst was applied to a silica support by means of a
two-stage incipient wetness impregnation. A vanadium oxalate
solution was brought to a volume of 900 mL by adding 0.9 M oxalic
acid to 1.1 mol of solid V.sub.2O.sub.5. The suspension was stirred
and heated to 80.degree. C. Solid oxalic acid dihydrate was added
stepwise to the suspension until the color changed from orange to
green to deep blue. The resulting solution was diluted to a total
volume of one liter with 0.9 M oxalic acid. The final solution was
2.2 M with respect to vanadium (V).
[0229] 41.71 mL of this vanadium oxalate solution were diluted to a
volume of 42 mL with deionized water, corresponding to 100% of the
liquid absorption capacity of the support. 50 g of silica (Cariact
Q20-C, 1-1.6 mm gap) were impregnated with the vanadium solution.
The resulting solid material was dried in a drying oven at
80.degree. C. overnight. In a second step, 21.02 g of 85%
phosphoric acid were diluted to 42 mL with deionized water and
impregnated onto the solid material. The resulting solid material
was dried in a drying oven at 80.degree. C. overnight. The
resulting solid material was calcined in accordance with the
following temperature profile:
[0230] i) heating from room temperature to 260.degree. C. at a rate
of 1.degree. C. per minute;
[0231] ii) heating at 260.degree. C. for 2 hours.
II.2 Catalyst 2
[0232] Oxidic catalyst comprising phosphorus and tin on
beta-zeolite support
II.2.1 Preparation of a Boron-Containing Zeolitic Material Having a
BEA Base Skeleton Structure
[0233] 209 kg of deionized water were provided in a vessel. While
stirring at 120 rpm (revolutions per minute), 355 kg of
tetraethylammonium hydroxide were added and the suspension was
stirred at room temperature for 10 minutes. Subsequently, 61 kg of
boric acid were suspended in this water and the suspension was
stirred at room temperature for a further 30 minutes. Subsequently,
555 kg of Ludox.RTM. AS-40 were added and the resulting mixture was
stirred at 70 rpm at room temperature for a further hour. The
liquid gel had a pH of 11.8, as measured with a pH electrode. The
final mixture obtained was transferred into a crystallization
vessel and heated to 160.degree. C., at a pressure of 7.2 bar,
while stirring (140 rpm) within 6 h. Subsequently, 61 kg of boric
acid were suspended in water and the suspension was stirred at room
temperature for a further 30 minutes. Subsequently, 61 kg of boric
acid were suspended in water and the suspension was stirred at room
temperature for a further 30 minutes. Then the mixture was cooled
to room temperature. The mixture was heated again to 160.degree. C.
within 6 h and stirred at 140 rpm for a further 55 h. The mixture
was cooled down to room temperature and then heated to a
temperature of 160.degree. C. while stirring at 140 rpm for a
further 45 h. 7800 kg of deionized water were added to 38 kg of
this suspension. The suspension was stirred at 70 rpm, and 100 kg
of a 10% by weight aqueous HNO.sub.3 solution were added. The
boron-containing zeolite material having a BEA skeleton structure
was separated from this suspension by filtration. The filtercake
was washed with deionized water at room temperature until the wash
water had a conductivity of less than 150 microsiemens/cm. The
filtercake thus obtained was dried in a nitrogen stream.
[0234] The zeolitic material thus obtained was subjected to a spray
drying operation in a spray tower with the following spray drying
conditions:
[0235] Drying gas, nozzle gas: technical grade nitrogen
[0236] Drying gas temperature: [0237] spray tower temperature
(inside): 235.degree. C. [0238] spray tower temperature (outside):
140.degree. C.
[0239] Nozzle: [0240] Top component nozzle supplied by Gerig; size
0 [0241] Nozzle gas temperature: room temperature [0242] Nozzle gas
pressure: 1 bar
[0243] Mode of operation: nitrogen direct
[0244] Apparatus used: spray tower with a nozzle
[0245] Configuration: spray tower-filter-scrubber
[0246] Gas flow rate: 1500 kg/h
[0247] Filter material: Nomex.RTM. needle-felt 20 m.sup.2
[0248] Metering via flexible peristaltic pump: SP VF 15 (supplier:
Verder)
[0249] The spray tower comprised a vertical cylinder having a
length of 2650 mm and a diameter of 1200 mm, with conical narrowing
of the cylinder at the base. The length of the cone was 600 mm. At
the top of the cylinder were disposed the atomization devices (a
two-phase nozzle). The spray-dried material was separated from the
drying gas in a filter downstream of the spray tower, and the
drying gas was conducted through a scrubber. The suspension was
conducted through the inner orifice of the nozzle, and the nozzle
gas was conducted through the annular slot that surrounded the
orifice.
[0250] The spray-dried material was then calcined at 500.degree. C.
for 5 h. The calcined material had a molar B.sub.2O.sub.3:SiO.sub.2
ratio of 0.045, a total organic carbon (TOC) content of 0.08% by
weight, a crystallinity determined by XRD of 100%, and a specific
BET surface area determined to DIN 66131 of 498 m.sup.2/g.
II.2.2 Deboronation--Formation of Vacant Tetrahedral Sites
[0251] 840 kg of deionized water were provided in a vessel provided
with a reflux condenser. While stirring at 40 rpm, 28 kg of the
spray-dried and calcined zeolitic material were added as described
above in II.2.1. Subsequently, the vessel was closed and the reflux
condenser was put into operation. The stirring rate was increased
to 70 rpm. While stirring at 70 rpm, the contents of the vessel
were heated to 100.degree. C. within one hour and kept at this
temperature for 20 h. Then the contents of the vessel were cooled
to a temperature below 50.degree. C.
[0252] The resulting deboronated zeolitic material having a BEA
skeleton structure was separated from the suspension by filtration
under a nitrogen pressure of 2.5 bar and washed with deionized
water four times at room temperature. After filtration, the
filtercake was dried in a nitrogen stream for 6 h.
[0253] The resulting deboronated zeolitic material, after
resuspension in deionized water, was spray-dried under the
conditions mentioned above in II.2.1. The solid content of aqueous
suspension was 15% by weight, based on the total weight of the
suspension. The zeolitic material obtained had a molar
B.sub.2O.sub.3:SiO.sub.2 ratio of less than 0.002, a crystallinity
determined by XRD of 77%, and a specific BET surface area
determined to DIN 66131 of 489 m.sup.2/g.
II.2.3 Synthesis of an Sn Beta-Zeolite
[0254] 200 g of the deboronated zeolitic material having a BEA
skeleton structure according to II.2.2 were combined in a mill
(mill type: Microton MB550) with 56.8 g of tin(II) acetate
(Sn(OAc).sub.2 [CAS no.: 638-39-1]), and the mixture was ground at
14 000 rpm (revolutions per minute) for 15 minutes. After the
grinding, the mixture was transferred to a porcelain basket and
calcined under air at 500.degree. C. at a heating rate of 2 K/min
for 3 h.
[0255] The powder material obtained had an Sn content of 14.4% by
weight, a silicon (Si) content of 38% by weight and a TOC of less
than 0.1% by weight.
II.2.4 Production of a Tin-Containing Material Having BEA Skeleton
Structure with Acid Treatment
[0256] 200 g of zeolitic material obtained according to II.2.3 were
provided in a round-bottom flask, and 6000 g of 30% by weight
aqueous HNO.sub.3 solution having a pH in the range from 0 to 1
were added. The mixture was stirred at a temperature of 100.degree.
C. for a time span of 20 h (200 rpm). The suspension was filtered
and the filtercake was then washed with deionized water at room
temperature until the wash water had a pH of about 7.
[0257] The zeolitic material obtained was dried at 120.degree. C.
for 10 h and calcined by means of heating to 550.degree. C. (2
K/min) and then heating at 550.degree. C. for 10 h. The dried and
calcined zeolitic material had an Si content of 36% by weight and
an Sn content of 14.0% by weight. In addition, the zeolitic
material had a specific BET surface area determined to DIN 66131 of
402 m.sup.2/g.
II.2.5 Preparation of a P-Treated Sn-Containing Material Having a
BEA Skeleton Structure
[0258] 191 g of the zeolitic material obtained according to II.2.4
were mixed with 23.88 g of ammonium dihydrogenphosphate
(NH.sub.4H.sub.2PO.sub.4). 149.6 g of deionized water were added
and mixed carefully. The suspension was dried in a vacuum oven at
110.degree. C. for 12 h. The dried material was calcined in an oven
heated to 500.degree. C. with a temperature ramp of 2 K/min under
air for 5 h. Subsequently, the dried and calcined material was
cooled to room temperature. 214 g of Sn-containing material having
a BEA skeleton structure were obtained.
[0259] The Sn-containing zeolitic material having BEA skeleton
structure had the following composition: 12.7% by weight of Sn, 32%
by weight of Si, <0.1% by weight of C (TOC), 2.8% by weight of
P. The BET surface area was determined to be 267 m.sup.2/g in
accordance with DIN 66131.
II.2.6 Forming of the P-Treated Sn-Containing Material with BEA
Skeleton Structure
[0260] A kneader was charged with 200 g of the zeolitic material
obtained according to II.2.5 and mixed with an acidic solution
prepared from 6 g of HNO.sub.3 (65% by weight) dissolved in 20 mL
of distilled water. The suspension was mixed (kneaded) for 10 min.
Added to the resulting mixture were 10 g of Walocel.TM. and 26.3 g
of Ludox.RTM. AS-40, and the mixture was mixed for a further 30
min. Finally, 120 mL of distilled water were added to the mixture
and mixed for a further 20 min. The paste was then extruded in a
Loomis extruder. Extrudates of 2.0 mm were obtained in a static
oven and dried at 120.degree. C. for 5 h, followed by calcination
at 500.degree. C. for 5 h under air at a heating rate of 2 K/min.
The resulting extrudates were divided into a fraction of 1.0-1.6
mm.
[0261] The calcined extrudates had a bulk density of 490 g/L with a
mechanical strength of 3 N. The elemental composition was Sn 12.7%
by weight, Si 34% by weight and TOC<0.1% by weight and P 2.8% by
weight.
II.3 Catalyst 3
Oxidic Catalyst Comprising Vanadium, Tungsten, Phosphorus and
Bismuth on Silica Support
[0262] 67 g of bismuth acetate were added to an aqueous citric acid
solution (100 g of acid in 1 liter of deionized water). The mixture
was heated to 80.degree. C. and stirred for 30 minutes. 117.5 g of
phosphoric acid (85%), 116 g of a colloidal silica suspension
(Ludox AS 40) and 100 g of ethylene glycol were added successively.
The mixture was stirred at 80.degree. C. for a further 30 minutes.
110 g of ammonium metavanadate and 169 g of ammonium metatungstate
were added successively. 20 g of acetyl cellulose were slurried
with deionized water and added to the mixture. The final mixture
was stirred at 80.degree. C. for three hours. The mixture was
concentrated in a rotary evaporator at 60.degree. C. and 45 mbar.
The resulting solid material was dried further in a drying oven at
100.degree. C. for 16 h.
[0263] The resulting solid material was calcined in accordance with
the following temperature profile:
[0264] i) heating from room temperature to 160.degree. C. at a rate
of 10.degree. C. per minute;
[0265] ii) heating at 160.degree. C. for 2 hours;
[0266] iii) heating from 160.degree. C. to 250.degree. C. at a rate
of 3.degree. C. per minute;
[0267] iv) heating at 250.degree. C. for 2 hours;
[0268] v) heating from 250.degree. C. to 300.degree. C. at a rate
of 3.degree. C. per minute;
[0269] vi) heating at 300.degree. C. for 6 hours;
[0270] vii) heating from 300.degree. C. to 450.degree. C. at a rate
of 3.degree. C. per minute;
[0271] viii) heating at 450.degree. C. for 6 hours.
II.4 Catalyst 4
Oxidic Catalyst Comprising Vanadium, Tungsten, Phosphorus and
Bismuth on Silica Support
[0272] 167.5 g of ammonium metavanadate were added to 3 liters of a
20% by weight aqueous solution of citric acid. The mixture was
heated to 50.degree. C. and stirred until dissolution was complete.
116 g of a colloidal silica suspension (Ludox AS 40) were added,
followed by 227.8 g of ethylene glycol. The mixture was heated to
80.degree. C. and stirred for 30 minutes. 35.3 g of ammonium
metatungstate were dissolved in 500 mL of deionized water and added
dropwise to the mixture. The mixture was then stirred at 80.degree.
C. for 15 minutes. 347.2 g of bismuth nitrate hexahydrate were
dissolved in 480 mL of a 10% nitric acid solution. The acidic
bismuth solution was added dropwise to the previous mixture and
stirred at 80.degree. C. for 30 minutes, then cooled down to
30.degree. C. while stirring constantly. 1232 mL of a 2% solution
of methyl cellulose were added and then the mixture was stirred for
a further 30 minutes. Finally, 303.7 g of an 85% phosphoric acid
solution were added and the mixture was stirred for 30 minutes. The
resulting mixture was dried at 80.degree. C. in a drying oven for
48 h.
[0273] For safety reasons, the resulting solid material was
calcined in an atmosphere having 3% by volume of O.sub.2/97% by
volume of N.sub.2 in accordance with the following temperature
profile:
[0274] i) heating from room temperature to 160.degree. C. at a rate
of 10.degree. C. per minute;
[0275] ii) heating at 160.degree. C. for 2 hours;
[0276] iii) heating from 160.degree. C. to 250.degree. C. at a rate
of 3.degree. C. per minute;
[0277] iv) heating at 250.degree. C. for 2 hours;
[0278] v) heating from 250.degree. C. to 300.degree. C. at a rate
of 3.degree. C. per minute;
[0279] vi) heating at 300.degree. C. for 6 hours;
[0280] vii) heating from 300.degree. C. to 450.degree. C. at a rate
of 3.degree. C. per minute;
[0281] viii) heating at 450.degree. C. for 6 hours.
III. Setup and Operation of the Pilot Plant
III.1 Example 1: Determination of the Maximum Amount of Acrylic
Acid in Stream S1
[0282] The apparatus consisted of a fixed bed reactor (bed length
about 90 cm, diameter 16 mm, 1.4541 stainless steel) heated in four
zones and having 3 sampling points for online GC measurements
(inlet, middle, outlet) and two reactant metering zones. In order
to charge the plant with formaldehyde and acetic acid, the
reservoir vessel was initially charged with acetic acid or acetic
acid solution and formaldehyde or formalin solution.
[0283] Formalin (49% by weight of formaldehyde in water) was
conveyed by means of a Fink HPLC pump and evaporated completely by
means of a microevaporator (passage length 60 mm, passage width 0.2
mm, alloy 22, 2.4602) (wall temperature about 280.degree. C.). In
order to prevent paraformaldehyde from precipitating out in the
cold conduit, the reservoir vessel and the distance up to the
evaporator were heated to 60.degree. C. By means of a three-way
tap, it was possible to run formalin either in a circuit back into
the vessel or else in the evaporator direction.
[0284] A Fink HPLC pump was used to pump acetic acid into a helical
tube evaporator (diameter 8 mm, length about 2 m, 1.4571 stainless
steel), which completely evaporated therein (wall temperature about
200.degree. C.) and mixed with a stream comprising nitrogen.
[0285] The stream comprising the evaporated formalin and the stream
comprising the evaporated acetic acid and nitrogen were combined
and passed as stream S1 via a pipeline heated to 150-200.degree. C.
through a static mixer (diameter 10 mm, length 80 mm, 1.4541
stainless steel) containing wire mesh into the reactor heated to
320.degree. C. (outer wall) (WHSV: 1.4 kg/kg/h). After passing
through an unfilled region (length 2.8 cm), the gas stream arrived
at a first steatite bed (mass 33 g, bed height 16 cm, 4-5 mm
balls). The downstream catalyst bed was divided into two (mass of
each 40 g, bed height 23 cm) and was interspersed with a second
steatite bed (mass 42 g, bed height 20 cm, 4-5 mm balls). The
overall bed rested on a catalyst support of about 3 cm in height,
with a third steatite bed (mass 14 g, bed height 7 cm, 4-5 mm
balls) concluding the reactor outlet. Within the reactor was a
thermowell of thickness 3.17 mm, which was used to measure a
temperature profile along the reactor. The reaction was conducted
at a pressure of 1100 mbar (absolute).
[0286] The reactor offgas was passed to a total combustion unit
downstream of the reactor outlet. For protection against blockages
by catalyst dusts, a filter station was installed downstream of the
reactor outlet. In the total combustion unit, all components were
incinerated with air metered in additionally (about 2000 L (STP)/h)
and nitrogen which can be metered in additionally (about 1000 L
(STP)/h) to give water and carbon dioxide. Constant pressure
conditions in the reactor over different test runs were established
by partly throttling the valves in the filter station. The total
combustion unit air was heated to 300-400.degree. C. by means of
heating sleeves. The combustion temperature in the combustion
catalyst bed varied with the organic carbon loading of the reactor
offgases and was between 250.degree. C. and 500.degree. C. The
offgas from the total combustion unit was passed through a
separator (T=5-15.degree. C.). The offgas that remains thereafter
was passed into the offgas conduit.
[0287] Acrylic acid (ACR) was added to the acetic acid-comprising
stream in different contents (ACR content, ACR input). Various
catalysts were used. The individual streams were analyzed by gas
chromatography. The results, and details of ACR contents, are shown
in tables 1 to 4 below, and presented in graph form in FIGS. 2 and
3. Since stream S1 was entirely gaseous, rather than the molar
figures for the ratio of acrylic acid to the sum total of
formaldehyde+acetic acid, the figures are given in % by volume.
TABLE-US-00001 TABLE 1 Catalyst 1 Ratio Yield of Yield Selectivity
Selectivity of acrylic acid acrylic of acrylic for acrylic for
acrylic to sum total of acid based acid acid based acid
formaldehyde + on formal- based on Formal- Acetic on formal- based
on acetic acid at dehyde acetic acid dehyde acid dehyde acetic acid
Exper- reactor inlet conversion conversion conversion conversion
conversion conversion iment [vol/vol] Mean [%] Mean [%] Mean [%]
Mean [%] Mean [%] Mean [%] Cat1-A 0.014 30.77 36.78 46.96 48.45
65.52 75.91 Cat1-B 0.036 30.37 33.19 46.62 45.03 65.14 73.71 Cat1-C
0.063 29.95 32.53 44.53 44.61 67.26 72.92 Cat1-D 0.090 23.95 26.53
44.12 41.24 54.28 64.33
TABLE-US-00002 TABLE 2 Catalyst 2 Ratio Yield of Yield Selectivity
Selectivity of acrylic acid acrylic of acrylic for acrylic for
acrylic to sum total of acid based acid acid based acid
formaldehyde + on formal- based on Formal- Acetic on formal- based
on acetic acid at dehyde acetic acid dehyde acid dehyde acetic acid
Exper- reactor inlet conversion conversion conversion conversion
conversion conversion iment [vol/vol] Mean [%] Mean [%] Mean [%]
Mean [%] Mean [%] Mean [%] Cat2-A 0.032 2.7 3.07 2.5 9.9 32.43
Cat2-B 0.072 1.98 1.83 6.14 10.38 36.30 18.00 Cat2-C 0.098 1.35
1.45 1.38 7.58 34.20 24.20 Cat2-D 0.018 3.628 3.158 8.38 11.08
40.26 32.15
TABLE-US-00003 TABLE 3 Catalyst 3 Ratio Yield of Yield Selectivity
Selectivity of acrylic acid acrylic of acrylic for acrylic for
acrylic to sum total of acid based acid acid based acid
formaldehyde + on formal- based on Formal- Acetic on formal- based
on acetic acid at dehyde acetic acid dehyde acid dehyde acetic acid
Exper- reactor inlet conversion conversion conversion conversion
conversion conversion iment [vol/vol] Mean [%] Mean [%] Mean [%]
Mean [%] Mean [%] Mean [%] Cat3-A 0.025 18.43 17.46 32.26 30.9
60.36 56.81 Cat3-B 0.048 14.6 20.51 21.76 29.33 77.61 75.20 Cat3-C
0.068 14.4 20.02 28.68 31.71 55.63 66.33 Cat3-D 0.090 12.32 17.83
38.98 31.13 37.04 61.43 Cat3-E 0.027 14.53 19.14 23.03 31.47 56.34
62.03
TABLE-US-00004 TABLE 4 Catalyst 4 Ratio Yield of Yield Selectivity
Selectivity of acrylic acid acrylic of acrylic for acrylic for
acrylic to sum total of acid based acid acid based acid
formaldehyde + on formal- based on Formal- Acetic on formal- based
on acetic acid at dehyde acetic acid dehyde acid dehyde acetic acid
Exper- reactor inlet conversion conversion conversion conversion
conversion conversion iment [vol/vol] Mean [%] Mean [%] Mean [%]
Mean [%] Mean [%] Mean [%] Cat4-A 0.030 27.83 27.21 42.63 40.28
65.34 67.55 Cat4-B 0.053 29.12 30.11 38.11 38.93 77.53 77.26 Cat4-C
0.076 26.80 32.73 32.59 37.31 82.55 82.34 Cat4-D 0.038 24.54 29.79
34.35 39.60 71.85 75.72 Cat4-E 0.102 12.91 14.93 45.56 51.47 30.21
32.42
[0288] As can be seen from the above tables 1-4 and especially
shown by FIGS. 2 and 3, the presence of acrylic acid in stream S1
was acceptable for the acrylic acid production in a molar ratio
relative to the sum total of the reactants, formaldehyde and acetic
acid, up to a value of 0.3:1. It was apparent that preferred molar
ratios of acrylic acid to the sum total of the reactants,
formaldehyde and acetic acid, in stream S1, were in the range of up
to 0.1:1, more preferably of up to 0.09:1, further preferably of up
to 0.08:1, further preferably of up to 0.07:1.
III.2 Example 2: Determination of the Minimum Acrylic Acid Content
in Stream S1
[0289] The example which follows was run with the aid of the
process simulation program CHEMASIM from BASF. The essential
compositions and properties of the streams shown in FIG. 1 can be
found in tables 5 and 6. Mass balances are completed by any offgas
streams not mentioned/shown.
[0290] The acetic acid and formalin solution reactants (.about.49%
by weight of formaldehyde, .about.49% by weight of water, .about.2%
by weight of methanol) were subjected to total evaporation (i) in a
suitable heat transferer, diluted with inert gas (nitrogen), and
fed as stream S1, optionally after mixing with the recycled streams
S2b_rec and/or S3 and/or S5 and/or S8, in gaseous form to the
reaction zone (ii), charged with the aldol condensation
reactor.
[0291] In the reaction zone (ii), stream S1 was contacted at
370.degree. C. and 1.1 bar absolute with a catalyst of the
empirical formula VO(PO).sub.4 shaped into cylindrical extrudates
having a cross-sectional area diameter of 3 mm and an average
length of 20 mm. This was done using a shell and tube reactor, with
the catalytically active fixed bed within the catalyst tubes,
around which fluid heat carrier flowed.
[0292] The gaseous reactor output S2 was cooled down to about
40.degree. C. in a suitable heat transferer in (iii), and partly
condensed at the same time. The uncondensed portion S2b which
comprised predominantly low-boiling components and inert gases,
after removing at least a portion of S2b, S2b_Purge, was recycled
upstream of the reactor in (ii) as S2b_Rec.
[0293] The condensed portion of S2, S2a, was guided into a
distillation column in (iv.1). This column was designed as a tray
column equipped with a number of crossflow trays equivalent to
about 30 theoretical plates, and was operated in rectificative
mode. The feed stream was at about the 10th theoretical plate. A
return stream consisting of at least a portion of S3 (not shown in
FIG. 1) was applied to the uppermost tray. The vapor from the
evaporator (not shown in FIG. 1) which was executed as a shell and
tube circulation evaporator and was operated with 4 bar steam as
heat carrier was conducted into the column below the first tray.
The column in (iv.1) was operated at a top pressure of 1.3 bar
absolute; the bottom temperature was about 140.degree. C., and the
top temperature about 105.degree. C. The vapors from the column
were at least partly condensed in a shell and tube apparatus (not
shown in FIG. 1), with conduction of the liquid component into a
distillate collection vessel and division thereof into return
stream and distillate draw stream S3 therein. At the bottom of the
column in (iv.1), a liquid bottom stream S4 was withdrawn.
[0294] Stream S4 was passed into a distillation column in (iv.2).
This column was designed as a tray column equipped with a number of
dual-flow trays equivalent to about 20 theoretical plates, and was
operated in rectificative mode. The feed stream was at about the
8th theoretical plate. A return stream consisting of at least a
portion of S5 (not shown in FIG. 1) was applied to the uppermost
tray. The vapor from the evaporator (not shown in FIG. 1) which was
executed as a shell and tube circulation evaporator and was
operated with 4 bar steam as heat carrier was conducted into the
column below the first tray. The column in (iv.2) was operated at a
top pressure of 100 mbar absolute; the bottom temperature was about
105.degree. C., and the top temperature about 40.degree. C. The
vapors from the column were at least partly condensed in a shell
and tube apparatus (not shown in FIG. 1), with conduction of the
liquid component into a distillate collection vessel and division
thereof into return stream and distillate draw stream S5 therein.
Stream S5 was recycled upstream of the reactor in (ii). Acrylic
acid was drawn off in liquid form as S6 in the bottom of the column
in (iv.2).
[0295] Stream S3 was passed into a distillation column in (iv.3).
This column was designed as a column with random packing, equipped
with a random packing bed height equivalent to about 20 theoretical
plates, and was operated in rectificative mode. The feed stream was
at about the 5th theoretical plate. A return stream consisting of
at least a portion of S7 (not shown in FIG. 1) was applied to the
uppermost tray. The vapor from the evaporator (not shown in FIG. 1)
which was executed as a shell and tube circulation evaporator and
was operated with 4 bar steam as heat carrier was conducted into
the column below the first tray. The column in (iv.3) was operated
at a top pressure of 90 mbar absolute; the bottom temperature was
about 60.degree. C., and the top temperature about 40.degree. C.
The vapors from the column were at least partly condensed in a
shell and tube apparatus (not shown in FIG. 1), with conduction of
the liquid component into a distillate collection vessel and
division thereof into return stream and distillate draw stream S7
therein. Stream S7 was disposed of as wastewater in need of
treatment. At the bottom of the column in (iv.3), a liquid bottom
stream S8 was withdrawn and recycled completely upstream of the
reactor in (ii).
[0296] With reference to the overall simulation of the process
described in example 2, the influence of the amount of acrylic acid
recycled on the economic viability of the process was illustrated.
With the aid of the CHEMASIM process simulator and an in-house BASF
SE tool for realistic assessment of capital and operating costs of
chemical processes, the preparation costs for acrylic acid by the
process described in example 2 were examined as a function of the
amount of acrylic acid permitted in the recycle streams. The
relative value estimated for the acrylic acid preparation costs
(based on the costs at a molar ratio of acrylic acid to the sum
total of formaldehyde and acetic acid of 0.3:1 in the reactor
inlet) as a function of the molar ratio of acrylic acid to the sum
total of formaldehyde and acetic acid in the reactor inlet (S1) is
shown in FIG. 4. The rise in the preparation costs with a smaller
permitted ratio of acrylic acid to the sum total of the reactants
at the reactor inlet was attributable to a crucial degree to the
rising energy costs which are caused by the higher distillative
separation intensity and hence rising demand for steam and cooling
water in the column (iv.2).
[0297] It is apparent from the thermodynamic simulation that the
lower limit in the molar ratio of acrylic acid to reactants
(formaldehyde+acetic acid) in stream S1 was 0.005:1; the preferred
lower limit was seen to be a molar ratio of acrylic acid to
reactant in stream S1 of 0.02:1. Since stream S1 was entirely
gaseous, rather than the molar figures for the ratio of acrylic
acid to the sum total of formaldehyde+acetic acid, the figures were
given in % by volume.
TABLE-US-00005 TABLE 5 Stream bar (1/2) M Stream S1 Stream S2
Stream S2a Abbre- [kg/ [% by [% by [% by viation kmol] [kg/h] wt.]
[kg/h] wt.] [kg/h] wt.] Formaldehyde FA 30.03 20769 8.73 8307.7
3.49 8033.4 9.35 Acetic acid ACE 60.05 41540 17.46 16616 6.98 15672
18.24 Acrylic acid ACR 72.07 5538.7 2.33 32680 13.73 31475 36.63
Water H2O 18.02 24332 10.23 33565 14.11 30023 34.94 Methanol MEOH
32.04 552.1 0.23 220.8 0.09 180.5 0.21 Formic acid FAC 46.03 564.0
0.24 564.0 0.24 531.9 0.62 Propionic acid PRA 74.08 10.9 0.00 10.9
0.00 10.7 0.01 Carbon dioxide CO2 44.01 22160 9.31 27685 11.64
Oxygen O2 32.00 6763.4 2.84 2580.6 1.08 Carbon monoxide CO 28.01
Hydrogen H2 2.02 Nitrogen N2 28.01 115703 48.63 115703 48.63 Sum
total 237933 100.0 237933 100.0 85927 100.0 Volumetric flow rate V
m.sup.3/h 293553 375736 82.64 Density .rho. kg/m.sup.3 0.811 0.633
1039.7 Viscosity eta .eta. mPa s 0.027 0.027 0.997 Specific heat
c_p kJ/kg/K 1.387 1.398 2.901 Surface tension .sigma. N/m 0.039
Mean molar mass M kg/kmol 31.0 30.8 32.4 Temperature T .degree. C.
370.0 370.0 40.0 Boiling pressure BP bar Pressure p bar 1.400 1.100
1.400 Stream Stream Stream S2b S2b_Purge S2b_Rec Stream S3 [% by [%
by [% by [% by [kg/h] wt.] [kg/h] wt.] [kg/h] wt.] [kg/h] wt.]
Formaldehyde 274.3 0.18 51.7 0.17 206.6 0.17 8030.6 19.33 Acetic
acid 943.8 0.62 188.8 0.62 755.0 0.62 3287.0 7.91 Acrylic acid
1205.1 0.79 241.0 0.79 964.1 0.79 472.1 1.14 Water 3541.7 2.33
707.1 2.33 2828.5 2.33 29579 71.19 Methanol 40.4 0.03 6.8 0.02 27.2
0.02 179.9 0.43 Formic acid 32.2 0.02 6.4 0.02 25.7 0.02 0.1 0.00
Propionic acid 0.2 0.00 0.0 0.00 0.2 0.00 0.0 0.00 Carbon dioxide
27685 18.21 5537.0 18.21 22148 18.21 Oxygen 2580.6 1.70 516.1 1.70
2064.5 1.70 Carbon monoxide Hydrogen Nitrogen 115703 76.12 23141
76.12 92563 76.12 Sum total 152007 100.0 30401 100.0 121605 100.0
41549 100.0 Volumetric flow rate 94258 18852 75406 41.41 Density
1.613 1.613 1.613 1003.3 Viscosity eta 0.018 0.018 0.018 0.412
Specific heat 1.095 1.095 1.095 3.636 Surface tension 0.049 Mean
molar mass 29.9 29.9 29.9 21.0 Temperature 40.0 40.0 40.0 105.7
Boiling pressure 1.300 Pressure 1.400 1.400 1.400 1.300
TABLE-US-00006 TABLE 6 Stream bar (2/2) M Stream 54 Stream S5
Stream S6 Stream S7 Stream S8 Abbre- [kg/ [% by [% by [% by [% by
[% by viation kmol] [kg/h] wt.] [kg/h] wt.] [kg/h] wt.] [kg/h] wt.]
[kg/h] wt.] Formaldehyde FA 30.03 2.8 0.01 2.8 0.02 109.7 0.50
7920.9 40.40 Acetic acid ACE 60.05 12385 27.91 12331 70.82 54 0.20
0.0 0.00 3287.0 16.77 Acrylic acid ACR 72.07 31003 69.86 4102.4
23.56 26901 99.76 0.0 0.00 4721 2.41 Water H2O 18.02 443.8 1.00
443.8 2.55 0.0 0.00 21657 98.70 7920.9 40.40 Methanol MEOH 32.04
0.6 0.00 0.6 0.00 175.9 0.80 3.9 0.02 Formic acid FAC 46.03 531.7
1.20 531.7 3.05 0.0 0.00 0.1 0.00 Propionic acid PRA 74.08 10.7
0.02 0.5 0.00 10 0.01 0.0 0.00 Carbon dioxide CO2 44.01 Oxygen O2
32.00 Carbon monoxide CO 28.01 Hydrogen H2 2.02 Nitrogen N2 28.01
Sum total 44378 100.0 17413 100.0 26965 100.0 21943 100.0 19605
100.0 Volumetric flow rate V m.sup.3/h 48.80 16.92 28.40 22.23
17.81 Density .rho. kg/m.sup.3 909.3 1028.9 949.6 987.1 1101.0
Viscosity eta .eta. mPa s 0.293 0.880 0.377 0.665 1.284 Specific
heat c_p kJ/kg/K 2.900 2.449 2.348 4.166 2.929 Surface tension
.sigma. N/m 0.016 0.027 0.019 0.069 0.044 Mean molar mass M kg/kmol
66.0 58.3 72.0 18.1 25.6 Temperature T .degree. C. 139.6 40.0 106.4
40.0 62.0 Boiling pressure BP bar 1.490 0.310 Pressure p bar 1.490
0.100 0.310 0.090 0.185
* * * * *